As technical literature filed prior to the present invention, there are literature (reference is to be made to, for example, patent document 1: WO2009/157197, patent document 2: Japanese Patent Laid-Open Ser. No. 2011-51224, and patent document 3: Japanese Patent Laid-Open Ser. No. 2011-51227) disclosing a molding method of a resin molded product in which a core member is interposed between two resin sheets into a laminated product.
In patent document 1 to 3, two sheet-shaped parisons (corresponding to resin sheets) are supplied between split molds to form the sheet-shaped parisons in a contour along cavities of the split molds. Next, a beforehand molded reinforcing core member (corresponding to the core member) is inserted between the split molds and the reinforcing core member is welded onto one of the sheet-shaped parisons. Next, the split molds are clamped such that the reinforcing core member is welded onto the other one of the sheet-shaped parisons and the sheet-shaped parisons are welded onto each other, to mold a resin molded product in which the reinforcing core member and the sheet-shaped parisons are configured in one block. As a result, there is molded a resin molded product in which a core member is interposed between two resin sheets into a laminated product.
Incidentally, in patent document 1 to 3, the reinforcing core member is welded onto the sheet-shaped parisons formed in a contour along cavities of the split molds; hence, the sheet-shaped parisons are cooled by the split molds and are easily hardened, and the welding strength between the reinforcing core member and the sheet-shaped parisons is lowered depending on cases.
Under this circumstance, the development of a molding method capable of increasing the welding strength between the core member and the resin sheets has been regarded as necessary.
Incidentally, as technical literature filed prior to the present invention, patent document 4 (Japanese Patent Laid-Open Ser. No. 2008-222208) discloses a core board obtained by monoblock-pressing a laminated structure in which a first fibrous substrate, a thermoplastic foam core layer, and a second fibrous substrate are laminated in this order.
In patent document 4, the fibrous substrate includes entangled nonwoven fabric including a fibrous material and a resin binder, and the melting point of the resin element constituting the thermoplastic foam core layer is higher than that of the resin binder. As a result, while stably keeping the contour of the thermoplastic foam core layer even during the heating in the monoblock press, only the resin binder of the fibrous substrate is partly melted and the fibrous substrate is tightly fixed onto the surface of the thermoplastic foam core layer.